The present invention relates to changeover devices which take signals from two sources and route one set or the other to an output, and more particularly to a synchronous changeover device for a television studio using an electronic switch to automatically switch beteween sets of synchronization signals without a noticeable glitch when a fault occurs.
Prior art changeovers in the television industry incorporate an automatic changeover only if an input falls below a certain rms amplitude. This re-routing takes place through a set of relay contacts which may take many millisecondds to stop bouncing. This relay "chatter" is propagated throughout a television studio and causes loss of sync which appears as noise on a television monitor for approximately 100 lines or so. Further since these prior art changeovers look at the rms amplitude, a signal having a short duty cycle with high amplitude may be detected as equal to a signal having a long duty cycle with low amplitude. The result is that due to this lack of precision the changeovers may not detect all failure modes.
What is desired is a changeover device which automatically detects faults with a higher degree of assurance and switches signal sets without a noticeable glitch.